Currently, LTE-A (Long Term Evolution-Advanced) specifications are studied by 3GPP (3rd Generation Partnership Project). In LTE-A, it is requested to realize a higher-speed communication than LTE communication. For this reason, in the LTE-A, it has been decided to support a wider band than that for LTE (bandwidth that is over the LTE 20 MHz bandwidth and up to 100 MHz).
In LTE-A, for the purpose of maintaining compatibility with LTE as much as possible, carrier aggregation (CA) technology is employed. Regarding the CA technology, a communication device performs communication simultaneously using a plurality of frequency bands up to a 20 MHz bandwidth, which are called component carriers (CCs). Thus, the communication device can secure a bandwidth up to a 100 MHz bandwidth, and realizes high-speed and high-capacity communication using that bandwidth (see section 5.5 of Non-Patent Document 1).
The CA technology includes three methods classified by usage of frequency bands (frequency bands) to be used by CCs.
(1) Contiguous frequency bands are used in the same frequency band (frequency band) (Inter-band Contiguous CA).
(2) Dispersed frequency bands are used in the same frequency band (frequency band) (Inter-band Non-Contiguous CA).
(3) Frequency bands in different frequency bands (frequency bands) are used (Inter-band Non-Contiguous CA).
A conventionally-studied CA technology is as to communication between mobile station devices and one macrocell base station device. In the CA technology, PUCCH (physical uplink control channel) is transmitted from the mobile station using a single CC.
In the CA technology, PCC (primary component carrier) is defined as a CC used to transmit PUCCH, and SCC (secondary component carrier) is defined as a CC not used to transmit PUCCH.
In the conventional multicarrier communication, there is no concept of PCC/SCC, and it has been possible to independently use the same signal in two frequency bands. Additionally, when a new frequency band (frequency band) is added, transmission of PRACH is performed using that frequency band to be added, synchronization is made, and then a connection process is performed, thus making it possible to add the frequency band.
In communication using the CA technology, it is limited to the PCC, as the first CC, that enables a connection process (see section 7.5 of Non-Patent Document 1).
In the conventional CA technology, a mobile station device has performed communication using PCC and SCC for a single base station device. For this reason, in order to disconnect the SCC, the mobile station device transmits an SCC disconnection request notification to a base station device using the PCC. Based on the disconnection request notification received by the base station device, the base station device could disconnect the communication using the SCC performed by the base station device.